The present invention generally relates to an image display arrangement and more particularly, to a stereographic image display system such as a stereoscopic television or the like which utilizes parallax between the left and right eyes.
Various attempts have been made since very old times to realize three-dimensional images or stereographic images, and there are a large number of systems available therefor at present including laser hologram, etc. However, the systems that are successfully put into actual application as stereographic image display arrangements are currently limited to the following two systems. Each of these systems is based on a principle in which images for left and right eyes are separately displayed so as to bring about a false impression of stereoscope, or hallucinate viewers as if there were parallax due to a stereographic or solid object, based on the deviation between individual images composed on the retinas of a viewers' eyes, thereby effecting a virtual stereographic display of images.
The two systems referred to above are:
(1) The system in which images for left and right eyes are formed by plane-polarized light so that the polarization axes thereof are directed to form an angle of 90.degree. with respect to each other, and thus, the images are observed in a separated state by glasses with polarizing plates. This system is mainly adopted in stereoscopic movies for theaters.
(2) The system in which images for left and right eyes are alternately displayed through time division by alternately switching the opening or of the glasses that function by an electronic light valve, in synchronization with the period of display, and the intended stereographic image display is effected.
The system in item (1) is close to ideal, since the stereographic images obtained thereby are free from flickering, while the glasses with polarizing plates to be worn by the viewers are light and inexpensive. However, in this known system, two display devices and projecting devices are required in order to simultaneously project two images with different polarization axes at all times, thus resulting in an increase of the number of devices involved, with a consequent complication of operations, and therefore, this system is not suitable for domestic use in general.
On the other hand, in the system referred to in item (2), although some flickering is noticed due to the half reduction of the number of frames per second which enters the left and right eyes, the system is realistic in that the stereograhic image can be formed by one television set.
With respect to the system in item (2), a virtual stereographic display arrangement has conventionally been proposed utilizing a television set. A system in which glasses having an electronic light valve function are constituted by liquid crystal cells, thereby switching the glasses with the light valve function for opening or closing in synchronization with the frame frequency or the field frequency of the television set.
However, the above known system also has a problem in that each of the viewers must inevitably wear the glasses with the electronic light valve function. More specifically, such glasses are not only heavy and cause fatigue after wearing them for a long time, but such glasses also tend to be expensive due to provision of the light valve function, and the cost therefor becomes a considerable amount when they are purchased for a number of viewers.
Moreover, most of the glasses with the electronic light valve function tend to eye give rise to fatigue due to the fact that the intensity of the transmitted light largely varies following the opening or closing of the light valves. Meanwhile, in a practice which utilizes the polarized light, it is unavoidable to reduce the intensity of the transmitted light to less than half based on the principles of polarized light with a consequent defect that the displayed images appear to be dark. A light valve device which removes such a defect has also been proposed which utilizes dynamic-scattering mode (DSM) of nematic liquid crystal, but such a device cannot fully cope with the frame frequency for the image display, since the dynamic-scattering mode has a slow response speed.
Furthermore, in the system of item (2), it is necessary to have the open/close function of the electronically controlled light valves synchronized with the display of images for the left and right eyes respectively, and conventionally, the signal has been derived from the vertical synchronizing signal of the television circuit. However, if the above practice is to be applied to an existing television set, it is required either to remodel internal circuits of the television set or to separately provide an adapter with a tuner only for deriving the synchronizing signal. Such remodeling is very difficult to be made at home in general, while the adapter with a tuner is a considerable expense for the user to purchase.
Generally, in the conventional virtual stereographic or stereoscopic display system utilizing the television set as described above, since the number of frames per second which enters each of the left and right eyes following open/close functions of the light valves of the glasses is to be reduced to half as compared with that in the normal display, flickering is noticed which results in eye fatigue. In order to eliminate such a disadvantage, there has been proposed a practice to increase the number of frames per second for the display, but alteration of a standard for the frame frequency makes it difficult to maintain interchangeability with respect to existing devices, and is not considered to be practical.